Process for forming and acoustically connecting structures on a substrate

Abstract

The present invention describes a processes that builds an acoustic cavity, a chamber, and vent openings for acoustically connecting the chamber with the acoustic cavity. The dry etch processes may include reactive ion etches, which include traditional parallel plate RIE dry etch processes, advanced deep and inductively coupled plasma RIE processes. Three embodiments for connecting the chamber to the cavity from the top side of the substrate, e.g. by using pilot openings formed using at least a portion of the mesh as an etch mask, by forming the vent openings using at least a portion of the mesh as an etch mask, or by having the chamber intersect the vent openings as the chamber is being formed, illustrate how the disclosed process may be modified. By forming the cavity on the back side of the substrate, the depth of the vent holes is decreased. Additionally, using at least a portion of the micro-machined mesh as an etch mask for the vent holes makes the process self-aligning.

Description

BACKGROUND OF THE INVENTION[0001]The present invention is directed generally to micro-electromechanical Systems (MEMS) devices and, more particularly, to processes for forming chambers and cavities in a substrate and acoustically interconnecting such structures.[0002]The ability to form moving parts measured in microns has opened up a huge range of applications. Such moving parts typically take the form of a beam or mesh that may form, for example, a variable capacitor, switch, or other component. The recent ability to seal micro-machined meshes has lead to the fabrication of microphones and microspeakers. See, for example, International Publication No. WO / 01 / 20948 A2 published 22 Mar. 2001, entitled MEMS Digital-to-Acoustic Transducer With Error Cancellation, the entirety of which is hereby incorporated by reference.[0003]A sealed mesh can function as a movable plate of a variable capacitor, and therefore can operate as a microphone. For a sealed mesh to operate as a microspeaker, ...

AI Technical Summary

Benefits of technology

[0005]The present invention is directed to a process comprising reducing the thickness of a back side of a substrate in an area where vents are to be formed. A micro-machined mesh is released from a top side of the substrate. A vent opening is formed that connects the released mesh and the area of reduced thickness. Several embodiments of the invention are disclosed. In one embodiment, pilot openings are formed in the substrate in the area of reduced thickness by using at least a portion of the mesh as an etch mask. That assures proper alignment of the vent openings. Releasing of the mesh involves removal of a portion of substrate from beneath the mesh. While the mesh is being released, the vents are formed by expanding the size of the pilot openings.

[0006]According to another embodiment, the vent openings are formed after the mesh is released. In that embodiment, the mesh is released using an isotropic etch. After the mesh is released, the mesh is used as an etch mask for an anisotropic etch to form vent openings for connecting the chamber with the area of reduced thickness. Use of the mesh as an etch mask eliminates a lithography step and assures proper alignment of the vent openings.

[0008]A common step in the various embodiments of the invention is to reduce the thickness of the substrate in the area of the vent openings. That is accomplished by etching a large cavity; because the diameter of the cavity relative to the depth is large, this step can be carried out efficiently. Connecting to this cavity is accomplished from the top side of the substrate, e.g. by using pilot openings formed using at least a portion of the mesh as an etch mask, by forming the vent openings using the mesh as an etch mask, or by having the chamber intersect the vent openings as the chamber is being formed. Those embodiments that use the mesh as an etch mask eliminate a lithography step thereby increasing processing speeds. Those advantages and benefits, and others, will be apparent from the Detailed Description of the Invention herein below.

Problems solved by technology

Forming of vents by this technique is slow in that several hundred microns of substrate may need to be etched to reach the chamber beneath the sealed mesh and the diameter of the vent is small compared to its depth.

Additionally, there are registration problems in that it is necessary to work form the back side of the substrate where there are no landmarks, and hundreds of microns may need to be etched to reach a chamber that may measure in the tens of microns.

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